Mooring apparatus

ABSTRACT

A tethering arrangement for a water-borne object which is effective to absorb forces tending to cause positional displacements thereof and subsequently utilize the energy so absorbed to return the object to its original location. In a preferred embodiment, one or more elongate members each having a predetermined elasticity factor connecting the floating object to a fixed sub-surface point or structure, the overall length of each such member varying in accordance with the stresses imposed thereon by virtue of weather conditions and/or other environmental factors to which the floating object may be subjected. In addition, the constant flexing of the elastic members greatly inhibits the growth of marine organisms on the surface thereof, as well as eliminating the cyclic stress which leads to the failure of steel components due to work-hardening.

United States Patent Roehler, II

Apr. 24, 1973 1 MOORING APPARATUS FOREIGN PATENTS OR APPLICATIONS1,018,196 1/1966 Great Britain ..114/230 Primary Examiner-Richard E.Aegerter Assistant Examiner-Douglas D. Watts AlmrneyRichard S. Sciascia,Q. Baxter Warner and Howard J. Murray, Jr.

ABSTRACT A tethering arrangement for a water-borne object which iseffective to absorb forces tending to cause positional displacementsthereof and subsequently utilize the energy so absorbed to return theobject to its original location. In a preferred embodiment, one or moreelongate members each having a predetermined elasticity factorconnecting the floating object to a fixed sub-surface point orstructure, the overall length of each such member varying in accordancewith the stresses imposed thereon by virtue of weather conditions and/orother environmental factors to which the floating object may besubjected. In addition, the constant flexing of the elastic membersgreatly inhibits the growth of marine organisms on the surface thereof,as well as eliminating the cyclic stress which leads to the failure ofsteel components due to work-hardening.

1 Claim, 5 Drawing Figures Patented April 24, 1973 2 Sheets-Sheet 2Fig.3

Fig.

MOORING APPARATUS STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION The mooring of ships, buoys and otherfloating ob jects has engaged the attention of man since the earliesttimes. The simplest method, and one still extensively used, is merely totie one end of a rope or cable to the object to be moored, the other endof such rope or cable being secured to an anchor or other fixed point.Although effective under ordinary circumstances, the tethering membermay fail under highly adverse weather conditions, and, in any event, themoored object is usually free to drift about the fixed point to whichthe rope or cable is attached.

For certain purposes such wide freedom of movement of a tethered objectcannot be tolerated. One example is that of a buoy serving as a weatherstation to monitor wind speed and direction, air temperature, seasurface temperature, and barometric pressure. This derived data iscustomarily transmitted from the buoy at regular intervals in the formof a coded message. These messages are received and decoded at a centralpoint, and integrated into a network of world-wide reports which areused to analyze and forecast the weather over the geographical area ofinterest.

However, important meteorological and oceanographic data has been lost,and expensive buoys damaged, due to failure of the mooring apparatus toyield to high displacement forces while still remaining on station.Furthermore, buoy stability has been a serious problem, since variationsin the positional status of the buoy can result in unacceptableinaccuracies in the derived data.

SUMMARY OF THE INVENTION The present concept makes use of one or moretethering members for a floating object, such members having apredetermined factor of elasticity and being so arranged as to impart arestoring force to compensate for both linear and angular positionaldisplacements of the object tethered thereby. In a preferred embodiment,one or more electrical conductors are integrated into the assembly. Theinvention also contemplates the use of materials offering highresistance to the growth of many marine organisms on the surfacethereof, as well as a similar resistance to corrosion.

STATEMENT OF THE OBJECTS OF THE INVENTION One object of the presentinvention, therefore, is to provide improved means for tethering afloating object.

Another object of the invention is to provide means for stabilizing abuoy against both linear and angular positional displacements.

A further object of the invention is to provide tethering means for afloating object, such means having a predetermined degree of elasticity.

An additional object ofthe invention is to provide for the tethering ofa floating object by means which possesses a high degree of corrosionresistance and which also offers unusual resistance to the growth ofmarine organisms on the surface thereof.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of oneembodiment of the invention as applied to the stabilization of a weatherbuoy;

FIG. 2 is an elevational view of a modification of the apparatus of FIG.1 showing a pair of resilient mooring members mounted on sheaves;

FIG. 3 is a side view of one of the resilient members of FIG. 2 togetherwith a portion of its mounting structure;

FIG. 4 is a side view of a further embodiment of the invention in whichonly a single electrically-conductive resilient mooring member isutilized; and

FIG. 5 is a sectional view ofa portion of FIG. 4 taken along the line55.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although the invention isgenerally applicable to any environment in which a floating object is tobe tethered, it finds particular utility in connection with a buoy whichhas been designed and instrumented to serve as an Oceanographic DataCollection System (ODCS). Consequently, the concept will be describedhereinafter as forming part of such a system, but it will be understoodthat such description is illustrative only and is not to be taken asrestricting the use of the invention to such apparatus.

One type of ODCS is designed to provide meteorological and oceanographicdata to support surface, aircraft, rocket, and missile test operationsin a given range area. This ODCS is instrumented to measure wind speedand direction, air temperature, barometric pressure, sea surfacetemperature and wave height. It is further arranged to measuresub-surface temperature, current speed, and current direction at threedifferent depths. The data thus derived is stored in the buoy andtransmitted on command to a shore station, where it is customarilyrecorded for reduction by computer techniques.

An ODCS system designed to incorporate the present concept is shown inFIG. 1 of the drawings. It preferably comprises a surface buoy 10connected to a subsurface buoy 12 by a plurality of pliant members 14,16, 18 and 20, these members being composed. of material possessing apredetermined degree of elasticity selected in accordance with themaximum expected vertical displacement of surface buoy 10 due to waveaction.

In the illustrated embodiment, the sub-surface buoy 12 lies at a depthof feet, and is made up of an air tank 22 resting on a cradle consistingof two spacedapart parallel arms 24 and 26. Resilient members 14 and 20are shown attached to opposite ends of arm 24, while resilient members16 and 18 are attached to opposite ends of arm 26. In cross-section,therefore, the

geometrical figure formed by members 14, 16, 18 and 20 is a rectanglewith such members lying at the respective corners thereof.

The sub-surface buoy 12 is taut-moored by a steel cable 28 swiveled at29 to an anchor 30 shown lying at a depth of 2,800 feet. The anchor 30may be in the form of a concrete block, or, alternatively, it maycomprise a power supply such, for example, as a radioisotropic thermalgenerator. Carried on the cable 28 are three sensors 32, 34 and 36, eachof these sensors measuring water temperature, current speed and currentdirection, and being located at depths of 85 feet, 132 feet and 485feet, respectively. As illustrated in the drawing, data transmissioncables leading to their respective sensors are secured to thestrain-carrying cable 28 at regular intervals, but are themselvesstrainrelieved. Water-tight connectors (not shown) in these datatransmission cables allow for removal of any or all of the sensors 32,34 and 36 for replacement or repair.

Additional oceanographic sensors (not shown) may be mounted on thesub-surface buoy 22 to measure water temperature as well as wave height.Associated therewith on the sub-surface buoy 22 are two self-containedbattery-operated pingers which assist in locating the sub-surface buoyshould the surface buoy break free during adverse weather conditions.

Several meteorological sensors 38 are mounted in a group 9 feet abovethe waterline on a quadrapod mast I 40 rising from buoy 10, this groupalso including radar corner reflectors, the transmit/receive antenna,and the navigation light. The sea surface temperature sensor is in thebottom of buoy 10 at a depth of about 3 feet. All sequencing, memory,transmit and receive electronics and the battery power supplies arecontained within the body of buoy 10, the system being designed forapproximately' l2 months of continuous service before maintenance isnecessary.

The ODCS shown in FIG. 1 of the drawings incorporates a major designmodification of arrangements heretofore utilized, the result being anincrease in reliability and reduced vulnerability to damage. It residesin the manner in which the surface buoy 10 is tied to the sub-surfacebuoy 12, the conventional single cable being replaced by the four pliantmembers 14, 16, 18 and 20. As hereinbefore stated, these members may bein the form of cables composed of material possessing a predetermineddegree of elasticity. In one system which has proven to be satisfactoryunder normal operating conditions, the members 14, l6, l8 and are ofl-inch diameter natural rubber pre-loaded to approximately 800 pounds.This effectively maintains the surface buoy 10 directly over thesub-surface buoy 12, thereby protecting the electrical data-transmissioncable 42 between the buoys as well as the mooring hardware. In addition,this four-point suspension configuration has the effect of stabilizingthe surface buoy 10 against rotation in a horizontal plane, since thesubsurface buoy 12 is essentially unaffected by wind and wave action atits 60-foot depth.

It has been found that a particularly suitable material for use infabricating the tethering members 14, 16, 18 and 20 is natural rubber.In addition to being highly resistant to hardening or deterioration fromcontact with sea water, the constant flexing of the cable surfacegreatly inhibits marine growth, apparently due to the inability of manymarine organisms to gain a point of attachment thereto. Furthermore, animportant factor contributing tothe destruction of conventional mooringcomponents is the work hardening of the material through millions offlexures in the ocean environment. A natural rubber rod when flexedwithin its design limits has no such work hardening characteristic. Theflexures need not occur at the maximum tensile loads in conventionalmoorings for them to fail from this flexure mode.

Under certain circumstances it may not be necessary to provide the samehigh degree of stability to a floating object as is the case with thearrangement of FIG. 1 of the drawings. It is then feasible to employ theapparatus of FIGS. 2 and 3, in which a single resilient tethering member44 in the form of a continuous band which runs over a pair of sheaves 46and 48 respectively journalled in blocks 50 and 52,'the former beingsecured to a floating object 54 and the latter being connected to ananchor 56 by a rigid (non-elastic) cable 58. If increased control isdesired, a second continuous band 59 and its associated sheaves 59a and59b may be added along with double pulley blocks, as brought out in FIG.2. As before, the degree of resiliency of the member 44 will be chosenin accordance with the amount of positional displacement of the object54 which can be tolerated under the circumstances of the case.

One important advantage accruing from the employment of the continuousband 44 is that its areaof contact with the sheaves 46 and 48 may bereadily changed either by diver manipulation or as a natural result ofwave action on the floating object 54. This shifting of the wear surfaceof the band 44 results in a greatly increased life expectancy for theelastic member and minimizes maintenance problems.

It will be recognized that, unlike the arrangement of FIG. 1, the designof FIGS. 2 and 3 does not provide for the transmission of electricaldata from a sub-surface point to the floating object. If such arequirement exists, the embodiment of FIGS. 4 and 5 finds application.If data from a sensor 60 (for example) carried on a non-stretchablecable 62 is to be conducted to floating object 64, it can beaccomplished by means of a conventional conductor 66 leading to one end68 of a cable 70 having one or more separate hollow passages therein andcomposed of flexible material such, for example, as natural rubber, eachhollow passage being filled with an electrically-conductive substance 72in liquid form, such, for example, as mercury. FIG. 5 shows a possiblecross section. The conventional connection or contact at the upper end74 of this liquid column is such as to compensate for any change inheight of the column of conductive liquid as the rubber cable 70stretches or contracts. Alternatively, a separate reservoir ofconductive liquid may be utilized at the top of each passage. Such adesign eliminates any requirement for a separate data-transmission cablebetween points 68 and 74 in FIG. 4. The use of a mercury core alsoprovides a telemetry link by using inductively-coupled transducers (notshown) to feed the single core while employing sea water as the returnpath. In addition, sensor batteries can be trickle-charged coupling.

200-pound anchor with two one-inch natural rubber cables feet longtensioned to 200 pounds at 40-foot extension. The natural rubber ofwhich the cables were composed was found to greatly inhibit the harmonicstrumming which is caused by the shedding of water in a current streamover a long connector of this type. As to the modification of FIGS. 4and 5, one sample was cycled 500,000 times without loss of mercury orelectrical continuity.-

It will now be recognized that the preset invention provides a tetheringmember or members of simple design in which the mooring tension ispredeterminable and which will allow for unlimited cycling withoutappreciable variation in operating characteristics. Furthermore, the lowcost and low maintenance of the system is coupled with its corrosionresistance and freedom from fouling due to excessive marine growth. Whena plurality of resilient tethering members are utilized, the floatingobject may be almost completely stabilized, not only from drift but alsoagainst angular rotation due to wind and/or wave action.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

lclaim:

l. A stabilized oceanographic monitoring station comprising:

a surface weather buoy equipped to provide meteorological andoceanographic data;

four elongated resilient rubber members connected to said weather buoyand arranged to define a geometrical figure of rectangular cross-sectionwith the four members lying in the respective corners thereof; saidresilient members being comprised of one-inch diameter natural rubberpreloaded to approximately 800 pounds;

a sub-surface buoy connected to the lower ends of the four elongatedmembers at a predetermined depth; said sub-surface buoy adapted tosupport an air tank andoceanographic sensors;

a non-resilient cable connecting said sub-surface buoy to an anchor at apredetermined depth;

at least one oceanographic sensor carried on said non-resilient cable ata predetermined depth and electrically connected by a data transmissioncable to transmitting means mounted on said weather buoy whereby watertemperature, current speed and current direction may be monitored. I

1. A stabilized oceanographic monitoring station comprising: a surfaceweather buoy equipped to provide meteorological and oceanographic data;four elongated resilient rubber members connected to said weather buoyand arranged to define a geometrical figure of rectangular cross-sectionwith the four members lying in the respective corners thereof; saidresilient members being comprised of one-inch diameter natural rubberpreloaded to approximately 800 pounds; a sub-surface buoy connected tothe lower ends of the four elongated members at a predetermined depth;said sub-surface buoy adapted to support an air tank and oceanographicsensors; a non-resilient cable connecting said sub-surface buoy to ananchor at a predetermined depth; at least one oceanographic sensorcarried on said non-resilient cable at a predetermined depth andelectrically connected by a data transmission cable to transmittingmeans mounted on said weather buoy whereby water temperature, currentspeed and current direction may be monitored.